Turbine's Justin Quimby has been interviewed at D&D Online. Here's a
bit on authenticity:

OGaming: How true to the source material – rule books, player's guides,
novels, etc. – will the title be?

Justin Quimby: Consider this. Every time you attack in our game, you see
a d20 pop up on screen that tells you what you rolled. We've gone to incredible
lengths to be as true to the pen and paper experience as we can. Arrows do
1d6 damage. We have spells like fireball and magic missile. You could print
your character sheet out and with very few modifications be able to play the
tabletop version. We have all the ability scores, skills, feats… it
all works the same way it does in the original version. That's one of the
great things about having the Dungeons & Dragons license too. You don't
have to come up with some random name like "magic bolt" for the
incantations your wizard casts… you get to call it by the name D&D
fans recognize.